The present invention relates to an electronic throttle valve drive unit.
One of prior art electronic throttle valve drive units is disclosed, for example, in JP-A 2-30933.
This electronic throttle valve drive unit includes a first electromagnetic clutch of the normally closed type which is in engagement when no power is supplied, and a second electromagnetic clutch of the normally open type which is in disengagement when no power is supplied, the first electromagnetic clutch being interposed between an accelerator pedal and a throttle valve, and the second electromagnetic clutch being interposed between the throttle valve and a motor.
With such structure, if operation is made to supply power to the first and second electromagnetic clutches in the normal condition so as to open and close the throttle valve through the motor, and to shut off power to the first and second electromagnetic clutches in the abnormal condition, cruising of a motor vehicle is possible in directly opening and closing the throttle valve through the accelerator pedal.
However, the above operation cannot practically be obtained unless when returning to engagement from disengagement, the first electromagnetic clutch as interposed between the accelerator pedal and the throttle valve becomes in engagement in a predetermined relative rotation angle position wherein an accelerator pedal fully closed position corresponds to a throttle valve fully closed position.
By way of example, if, when an accelerator is fully opened, the first electromagnetic clutch is in engagement with the throttle valve fully closed, the throttle valve is difficult to open thereafter through the accelerator pedal. Additionally, if, when the accelerator is fully closed, the first electromagnetic clutch is in engagement with the throttle valve opened, the throttle valve is difficult to close thereafter through the accelerator pedal.
In order to avoid such state, it is possible to control, before engaging the first electromagnetic clutch, the relative rotation angle position of two clutch plates to its initial position through the motor. However, when the electromagnetic clutch falls in instantaneous engagement due to troubles such as impossible motor control and interrupted power supply of the electromagnetic clutch, this control may not provide sufficient measures.
It is, therefore, an object of the present invention to provide an electronic throttle valve drive unit which allows proper engagement of the two clutch plates of the first electromagnetic clutch interposed between the accelerator pedal and the throttle valve when the first electromagnetic clutch is returned to engagement from disengagement.